So when he is removed he gets nothing at all. Is put somewhere safe and is supervised, but no-one interacts with him at all. When he is calm and comes back to class he then completes his work. If time has run out then he completes it at break/lunch/home. While he is rewarded for bad behaviour he isn't going to stop. Most five year olds are desperate for some a grown up to be in control, they do not have a need for control at all. However if life has taught them so far that adults will hurt them (in all kinds of ways) then they will develop a way of coping which could be refusing to do what anyone says, just in case. He needs to learn that adults in school will not do what he wants and that he does have to do what they want. But this will take a long time, especially as he has already learned the opposite. Keep on with what you are doing, but be patient. It has take 5 years to create the child in front of you, he isn't going to change overnight.